FreeLists / si-list / [SI-LIST] Re: Decoupling for PLL (continued)

[Zhangkun <zhang_kun@xxxxxxxxxx>]

Chas

Ceramic cap is of no use. It is easy to resonate when low ESR caps are used.

Best Regards

Zhangkun
2004.9.6
----- Original Message ----- 
From: "Charles Grasso" <cgrassosprint1@xxxxxxxxxxxxx>
To: <zhang_kun@xxxxxxxxxx>
Cc: "si-list" <si-list@xxxxxxxxxxxxx>
Sent: Monday, September 06, 2004 9:36 AM
Subject: [SI-LIST] Re: Decoupling for PLL (continued)


> Dear Zhangun,
> 
> It just so happens that I have just been fighting a
> noise problem witha ferrite bead /capacitor combo.
> In my case it turned out that a low ESR ceramic cap
> was required rather than a large electrolytic.
> 
> Could this be the problem..
> 
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx
> [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of zhangkun 29902
> Sent: Saturday, September 04, 2004 4:25 PM
> To: cgrassosprint1@xxxxxxxxxxxxx
> Cc: si-list
> Subject: [SI-LIST] Re: Decoupling for PLL (continued)
> 
> 
> Chas
> 
> I used bead. It resonated below 1MHz for the capacitor is too many.
> 
> Best Regards
> 
> Zhangkun
> 2004.9.5
> 
> ----- Original Message -----
> From: Charles Grasso <cgrassosprint1@xxxxxxxxxxxxx>
> Date: Sunday, September 5, 2004 6:33 am
> Subject: [SI-LIST] Re: Decoupling for PLL (continued)
> 
> > Hi Zhangkun,
> > 
> > Its very important to differentiate between an inductor and a 
> > ferrite bead.
> > A ferrite bead typically has minimal impedance in the kHz range 
> > and really
> > only
> > starts to kick in in the 10s of MHz range. An inductor, on the 
> > other hand,
> > can
> > exhibit LARGE reative impedance in the kHz range (depending on the 
> > value) -
> > but
> > will also exhibit resonances that need to be damped.
> > 
> > Chas
> > 
> > -----Original Message-----
> > From: si-list-bounce@xxxxxxxxxxxxx
> > [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Zhangkun
> > Sent: Thursday, September 02, 2004 10:53 PM
> > To: si-list
> > Subject: [SI-LIST] Decoupling for PLL (continued)
> > 
> > 
> > Dear all
> > Recently, I have done some measurement. It is found that when the
> > bead(inductor) is used, the power ground noise at 333KHz from VRM 
> > is larger.
> > There is some noise near the clock frequency points.
> > 
> > For example, the output clock of PLL is 50MHz. At 50.333MHz and 
> > 49.667MHz,there is noise, which is in proportion to the noise at 
> > 333KHz. Maybe the PLL
> > modulates the noise of VRM into the output clock.
> > 
> > Is there any SPICE model for PLL?
> > 
> > Best Regards
> > 
> > Zhangkun
> > 2004.9.3
> > 
> > 
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